The present invention relates to power transmissions and, more particularly, to a family of transmissions having three planetary gear sets that are controlled by five torque transmitting mechanisms to provide at least six forward speed ratios and one reverse ratio.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times. The number of forward speed ratios that are available in the transmission determines the number of times the engine torque range is repeated. Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore, manually shifted (countershaft) transmissions were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration. It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. Six speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978, U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000, and U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992.
Six speed transmissions offer several advantages over four and five speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ power transmissions, such as Polak, having six or more forward gear ratios, passenger cars are still manufactured with three and four speed automatic transmissions and relatively few five or six speed devices due to the size and complexity of these transmissions. The Polak transmission provides six forward speed ratios with three planetary gear sets, two clutches and three brakes. The Koivunen patent utilizes six torque transmitting devices including four brakes and two clutches to establish the six forward speed ratios and another reverse speed ratio. The Lepelletier employs three planetary gear sets, three clutches and two brakes to provide six forward speeds. One of the planetary gear sets is positioned and operated to establish two fixed speed input members for the remaining planetary gear sets.
It is an object of the present invention to provide an improved family of transmissions providing at least six forward speed ratios and one reverse speed ratio.
In one aspect of the present invention, each family member has three planetary gear sets each having three members consisting of a sun gear member, a ring gear member, and a planet carrier assembly member. In another aspect of the present invention, each family member includes five torque transmitting mechanisms that are operable to control the ratios in the planetary gear sets. In yet another aspect of the present invention, a member in the first planetary gear set is continuously interconnected with a member of the second planetary gear set through a first interconnecting member, and another member of the second planetary gear set is continuously interconnected with a member of the third planetary gear set through a second interconnecting member.
In still another aspect of the present invention, one of the interconnecting members is continuously interconnected with a stationary portion of the transmission. In yet still another aspect of the present invention, a transmission input shaft is interconnected with a member of one of the planetary gear sets, and a transmission output shaft is continuously interconnected with a member of one of the planetary gear sets. In a further aspect of the present invention, the torque transmitting mechanisms are all of the rotating type torque transmitting mechanisms (clutches) that are selectively interconnectable between members of the planetary gear sets with; a first clutch selectively interconnecting a member of the first planetary gear set with a member of either the second or third planetary gear set; a second clutch selectively interconnecting a member of the first planetary gear set with either a member of the second planetary gear set, or a member of the third planetary gear set, or the input shaft, or the output shaft; a third clutch selectively interconnecting a member of the third planetary gear set with either a member of the first planetary gear set, or a member of the second planetary gear set, or the input shaft, or the output shaft; a fourth clutch selectively interconnecting a member of the third planetary gear set with either the second interconnecting member, or a member of the first planetary gear set, or a member of the second planetary gear set, or the input shaft, or the output shaft. A fifth clutch selectively interconnecting a member of the third planetary gear set with either another member of the third planetary gear set, or a member of the first planetary gear set, or a member of the second planetary gear set, or the input shaft, or the output shaft. In yet a further aspect of the present invention, the clutches are engaged in combinations of two to provide at least six forward speed ratios and one reverse speed ratio. In still another aspect of the present invention, the family members provide a low-content, low cost six and seven speed transmission mechanisms.
This invention describes low-content, low-cost six- and seven-speed transmission mechanisms having three planetary gear sets and five selectable torque transmitting mechanisms (clutches). Each of the three planetary gear sets has three members. The first, second or third member of each planetary gear set can be any one of sun, ring or planet carrier assembly. The planet carrier assembly can be single- or double-pinion.
A first member of the first planetary gear set and a first member of the second planetary gear set are continuously connected with a stationary member. A connecting member continuously connects a second member of the second planetary gear set with a first member of the third planetary gear set. The input and output shafts are continuously connected with members of the planetary gear sets.
A first clutch selectively connects a member of the first planetary gear set with the third member of the second planetary gear set or a member of the third planetary gear set. A second clutch selectively connects a member of the first planetary gear set with said second fixed interconnection, a member of the third planetary gear set, a member of the second planetary gear set, input shaft or output shaft.
A third clutch selectively connects a member of the third planetary gear set with a member of the first planetary gear set, a member of the second planetary gear set, input shaft or output shaft. A fourth clutch selectively connects a member of the third planetary gear set with the said second fixed interconnection, a member of the first planetary gear set, a member of the second planetary gear set, input shaft or output shaft. A fifth clutch selectively connects a member of the third planetary gear set with another member of the third planetary gear set, a member of the first planetary gear set, a member of the second planetary gear set, input shaft or output shaft.
The five selectable torque transmission devices (clutches) are engaged in combinations of two to yield at least six forward speed ratios and one reverse speed ratio.